Harmonic butterflies as a plasma diagnostic tool

Inductively coupled plasma-tools have three power-coupling modes:capacitive (E-mode), inductive (H-mode) and Helicon wave (W-mode). These vary in light output intensity and rf behaviour depending on the system parameters. Here the particular interest is in the rf fundamental and its plasma-generated harmonic amplitudes and the relative phase between them. For the DCU ARIS II and the QUB GEC reference cell we have observed that the rf fundamental and its plasma generated harmonic(s) vary in amplitude and relative phase with the mode of discharge coupling. The rf information is captured using either a non-invasive dual-direction coupler and/or a surface-wave probe, and is displayed as a Lissajous figure on an oscilloscope. Experiments show that this technique delineates the mode change both in time and space for argon, chlorine and oxygen discharges. In the case of self-pulsing the Lissajous figure forms a time-varying Butterfly image that follows the pulse period thus allowing the time varying discharge to be monitored in real-time. Partially funded by the HEA North-South Programme for Collaborative Research and by SFI under grant number 02/IN.1/I147.